docs: def abbreviate_sha1(cls, sha1):
          """Uniquely abbreviates the given SHA1."""
  
          # For now we invoke git-rev-parse(1), but hopefully eventually
          # we will be able to do this via pygit2.
          cmd = ['git', 'rev-parse', '--short', sha1]
          # cls.logger.debug(" ".join(cmd))
          out = subprocess.check_output(cmd, universal_newlines=True).strip()
          # cls.logger.debug(out)
          return out